Telephone line surge protector

ABSTRACT

A telephone line protection module having a printed circuit board base with conductive paths connected to pins of the module. Overvoltage sensitive semiconductor devices are soldered to the ends of a conductive bridge, and the bridge is spring-biased between a module cover and the conductive bridge. The semiconductor devices are thus forced into electrical contact with the printed circuit paths. In addition, in the event the semiconductor devices are thermally destroyed, the conductive bridge is forced by the spring into direct contact with the printed circuit paths.

BACKGROUND OF THE INVENTION

Telephone line protection devices have been required for many years bytelephone operating companies, and the like, in order to provideprotection to central office switching equipment from electrical strikesand power line crosses coupled to the telephone lines. At least onetelephone line protector is required for each telephone subscriber line.In view that many central office switching systems service thousands,and often hundreds of thousands of subscribers, many such protectionmodules are required. Each module is constructed of a standardized sizeand with five pins of a uniform configuration. Two pins are associatedwith the tip and ring telephone lines, two other pins are associatedwith the customer or equipment tip and ring lines, and a fifth pin isconnected to ground.

The basic function of a telephone line surge protection circuit is tosense an excessive voltage, such as 300 volts, on either the telephoneline tip or ring conductor, and very quickly connect such conductor toground to prevent the customer equipment from experiencing sustainedvoltages higher than such threshold. Specialized solid state devices aregenerally utilized for providing a high speed short circuit to ground. Ahost of other subsidiary features can be carried out by the protectiondevice, including fail-safe grounding in response to a thermal overload,open circuiting between the telephone line and customer lines, etc.

Because of the high demand for protection devices, a myriad of suchdevices are currently available. Illustrative of the many differentprotection device designs and modules are those set forth in U.S. Pat.Nos. 4,796,150 by Dickey et al.; 5,031,067 by Kidd et al; 5,172,296 byKaczmarek; and 5,357,568 by Pelegris. In all of these protection moduledesigns, there are many complicated parts which lead not only to greatercost, but also to reduced reliability. Importantly, because of thecomplicated nature of the components of the various modules, the manuallabor in assembling the modules is extensive, which only leads to a morecostly product.

It is well-known in the electronics industry to facilitate assembly ofmodules by mounting the components on printed circuit boards. Indeed,the printed circuit board manufacture as well as the automatic componentinsertion is well-established. The use of printed circuit boards inprotection devices is suggested in U.S. Pat. No. 5,175,662 by DeBalko etal. Various semiconductor devices and components are mounted on aprinted circuit board which, in turn, is connected by connector contactsto a module base. Although this design tends to be more efficient, itstill requires the additional expense of connectorizing the printedcircuit board as well as requires a molded plastic base for the module.The injection molding of the base members of many of the protectionmodules is a standard practice, as noted in U.S. Pat. No. 5,357,568 byPelegris. Disclosed in U.S. Pat. No. 5,442,519, also by DeBalko et al,is a pair of printed circuit boards that are utilized in a telephoneline protection module. However, one printed circuit board is stillconnected to a plastic base member by way of pin and socket connectors,thereby resulting in a relatively expensive unit. The use of plasticbase members is popular, primarily because of the ease of forming tabsat the peripheral edges thereof for snap-lock engagement withcorresponding holes in a protective cover. Such an arrangement is shownin the Dickey et al. patent identified above.

In many of the conventional telephone line protection modules,encapsulated semiconductor devices are utilized as overvoltage sensorsand switches. The reason for this is that such devices are generallyavailable from the manufacturer only in packaged or encapsulated form.Again, the additional processing of the devices to package the sameresults in a more expensive component, often when packaged devices arenot necessary. For example, when a semiconductor device is packaged soas to have pins, then often a corresponding socket is required. It canbe appreciated that the use of packaged components often leads to a moreexpensive product.

From the foregoing, it can be seen that a need exists for a new type ofprotection module that has few components, is easily assembled and ismuch less costly than the prior art modules. Another need exists for animproved telephone line protection module that employs a printed circuitboard as the base itself to which the module pins are inserted, therebyfacilitating both manufacture, assembly and cost. Another need existsfor a protection module design in which the protective cover can besnap-lock engaged directly to a printed circuit board base member.

SUMMARY OF THE INVENTION

In accordance with the principles and concepts of the invention, aprotection module is disclosed of the type that overcomes theshortcomings and problems attendant with the prior art designs. Inaccordance with the preferred embodiment of the invention, the telephoneline protection module includes a printed circuit board base member towhich five module pins are mounted. The printed circuit board is formedwith three general conductive areas, two for connecting the respectivetelephone line tip and ring conductors to the corresponding tip and ringcustomer equipment, and a third conductive path providing a groundconnection to the module circuits.

First and second unpackaged semiconductor wafer devices that areresponsive to overvoltage conditions are soldered to a conductive bridgemember. The center of the bridge member is then soldered to the printedcircuit board ground (connection, while the ends of the bridge membercause the semiconductor wafers to be forced into electrical contact withrespective printed circuit board tip and ring conductive paths. Agenerally C-shaped spring with curved ends is captured within webstructures of a housing cover so that when the cover is snap-fit to theprinted circuit board base, the spring wire bears down on the ends ofthe conductive bridge, thereby forcing the semiconductor wafer devicesinto contact with the respective tip and ring conductive paths. Afail-safe mechanism is provided, in that if either one of thesemiconductor wafers is thermally destroyed due to excessive currenttherethrough, the spring tension causes the conductive bridge to beforced into contact directly with the conductive path of the printedcircuit board. A telephone line protection module of very fewcomponents, and which is easily assembled, is thereby provided.

In accordance with a second embodiment of the invention, the module casedoes not snap-lock to the printed circuit board base, but rather has ahousing cover with a plastic post that protrudes through the base. Theend of the post can thus be melted and mushroomed to thereby secure thebase to the module cover.

BRIEF DESCRIPTION OF THE DRAWINGS

Further features and advantages will become apparent from the followingand more particular description of the preferred and other embodimentsof the invention, as illustrated in the accompanying drawings in whichlike reference characters generally refer to the same parts, elements orfunctions throughout the views, and in which:

FIG. 1 is an exploded view of the various components of the telephoneline protection module constructed according to the invention;

FIG. 2 is an isometric view of the printed circuit board base member,together with the semiconductor devices and the conductive bridgemember;

FIG. 3 is a side view of the printed circuit board base member and therelative position of a C-spring that is biased against the bridgemember;

FIG. 4 is an isometric view of the module cover shown in broken lines,and with the internal webbing structure shown in solid lines for holdingthe C-shaped spring;

FIGS. 5-8 are respective first side, top, bottom and second side viewsof the module cover constructed according to the invention;

FIGS. 9 and 10 are sectional views of the module cover, taken alonglines 9--9 and 10--10 of FIG. 6;

FIGS. 11a and 11b are cross-sectional views of the module cover showingthe internal webbing structure for supporting the C-shaped spring; and

FIG. 12 illustrates another embodiment of a module cover webbingstructure and base member.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 illustrates the various components of the telephone lineprotection device 10 constructed according to a first embodiment.According to an important feature, a base member 12 comprises a printedcircuit board having a first conductive path 14. A first bore 16 and asecond bore 18 are formed through the printed circuit board 12, as wellas through the conductive path 14. A pair of pins 20 and 22 associatedwith the telephone line ring conductor and the customer ring conductor,each include a reduced diameter shank, such as shown by referencenumeral 24. The reduced diameter portion 24 of the pin 22 fits withinthe respective bore 18 until stopped by the shoulder 26. The pin 22 canthen be soldered to the conductive path 14. The other pin 20 issimilarly secured and supported by the printed circuit board base 12. Asecond conductive path 28 is associated with a pair of pins 30 and 32,each associated with the telephone tip and customer tip lines. The pins30 and 32 are supported and electrically connected to the base 12 in themanner described above. Lastly, a third conductive path 34 is formedbetween the ring conductive path 14 and the tip conductive path 28. Aground pin 36 fits within a bore 38 and is electrically connected to thepath 34 in the manner described above. As can be appreciated, thespacing, arrangement and length of the various pins is standardized andwell-known in the art.

A first semiconductor device 40 and a second semiconductor device 42 areplaced into electrical contact with the respective ring conductive path14 and tip conductive path 28. As will be described more thoroughlybelow, the semiconductor devices 40 and 42 conduct current in abidirectional manner, and need not be packaged or encapsulated. Rather,the devices need only be "bare" semiconductor wafers having suitablecontact surfaces on opposing sides thereof. Preferably, eachsemiconductor device 40 and 42 comprises a overvoltage sensitive devicethat allows a bidirectional flow of current therethrough when athreshold voltage has been exceeded. General purpose overvoltagesensitive devices are disclosed in U.S. Pat. No. 5,479,031, assigned tothe assignee hereof.

A respective end of a conductive bridge member 44 is soldered to a topcontact of each semiconductor device 40 and 42 so as to sandwich thedevices between the bridge member 44 and the respective printed circuitboard conductive paths 14 and 28.

A C-shaped spring 46 having curved ends 48 and 50 applies downwardpressure on the opposing ends of the bridge member 44 to thereby forcethe semiconductor devices 40 and 42 into intimate contact with therespective conductive paths 14 and 28.

A module housing 52 molded with a plastic material is constructed toachieve a snap-lock engagement with the printed circuit board base 12.As will be described more thoroughly below, the housing 52 isconstructed internally to hold the spring 46 so that uniform pressurecan be applied to the semiconductor devices 40 and 42 via the bridgemember 44.

With reference now to FIG. 2, there is shown an enlarged view of thebase member of a portion of the telephone line protector module 10. Theprinted circuit board 12 is of conventional design, constructed of anepoxy and fiberglass composition. Other suitable materials on whichprinted circuit conductive paths can be formed can be employed in thefabrication of the invention. Preferably, the printed circuit board base12 is about 0.0625 inches thick. Etched or otherwise formed on thesurface of the printed circuit board 12 are the three conductive areas14, 28 and 34. The conductive areas are preferably formed of a heavycopper material sufficient to carry the requisite current. After themodule pins are inserted into the holes and held therein, the base canbe processed through a reflow solder machine so that the pins aresoldered to the respective conductive paths. Ideally, although not anecessity, a surface area in the middle of the conductive paths 14 and28 can be plated with a nonoxidizing conductive material, such as gold,and thereafter masked to prevent solder flow thereon. Such isolatedconductive paths provide an excellent contact to the respective bottomcontact area of the semiconductor devices 40 and 42.

As noted above, each semiconductor device 40 and 42 is preferably atriac-like device, in which current can be carried in either direction.In other words, each semiconductor device can conduct currenttherethrough, irrespective of the polarity of the overvoltage coupled tothe telephone line. Also, in order to make the module 10 furthercost-effective, the semiconductor devices 40 and 42 need not be packagedor encapsulated, but need only have suitable contacts on both top andbottom surfaces thereof. SIDACtor® semiconductor devices havingbreakdown voltages of about 275-350 volts, and which can carry currentsranging upwardly of 100 amps at a 10×1000 microsecond waveform, areobtainable from Teccor Electronics, Inc., Irving, Tex.

The conductive bridge 44 is preferably constructed of a strip of copperhaving two ends 60 and 62 connected by an intermediate offset section64. The extent by which the section 64 is offset with regard to the ends60 and 62 is substantially the same as the thickness of thesemiconductor devices 40 and 42. This allows the bottom surface of theoffset section 64 to be soldered to the ground conductive area 34without placing the bridge member 44 in tension or stress. Theconductive bridge 44 is constructed of a copper material of therequisite cross-sectional area so as to conduct a sufficient amount ofcurrent. While only one conductive bridge 44 is utilized, those skilledin the art may prefer to utilize a separate conductive bridge to connectthe semiconductor devices 40 and 42 to a ground path.

In accordance with an important feature, the top contact (not shown) ofeach semiconductor device 40 and 42 is soldered to the bottom surface ofthe respective conductive bridge arm 60 and 62. The bottom contact (notshown) of each semiconductor device 40 and 42 is not fixed to therespective conductive area 14 and 28, bat only makes a pressure contacttherewith. This reduces thermal stresses imparted to the semiconductordevices 40 and 42 due either to ambient temperatures or temperaturesgenerated by current flow through either the conduction path or thedevice. Alternatively, the semiconductor devices 40 and 42 can besoldered to the printed circuit board conductive areas, but not to theconductive bridge 44.

FIG. 3 illustrates the manner in which the semiconductor devices 40 and42 are spring-biased into electrical contact with the respectiveconductive surfaces 14 and 28 of the printed circuit board base 12. Agenerally C-shape spring 46 is formed as a cross-sectionally round,flat, rectangular or square wire. A phosphor bronze or other suitablespring material can be utilized. A major portion 70 of the spring 46 isformed in a semicircular arc of a first radius. The ends 48 and 50 ofthe spring 46 also constitute semicircular arcs, each having a radiusthat is substantially smaller than the radius of the spring portion 70.Midsections 72 and 74 of the respective spring ends 48 and 50 bear downupon the respective ends 60 and 62 of the conductive bridge 44. Withthis arrangement, intimate contact is provided between the bottomcontact of the semiconductor devices 40 and 42 and the respectiveprinted circuit board conductive paths 14 and 28.

The spring 46 not only provides the pressure to achieve a reliablesemiconductor device contact to the conductive paths 14 and 28, but alsoexerts a sufficient force to "crush" the semiconductor devices shouldthermal destruction thereof occur. Depending upon the amount of energyimparted into a telephone line by a power line cross or a lightningstrike, the current carried by one or both of the semiconductor devices40 and 42 may cause a thermal destruction thereof. In other words, thecurrent conducted by the device can literally melt the semiconductormaterial. Should this type of thermal destruction occur, the forceapplied by the spring 46 to the semiconductor device causes theliquefied semiconductor material to disburse outwardly, thereby forcingthe conductive bridge end into direct contact with the conductive pathof the printed circuit board 12. When this occurs, the telephone line ismaintained in a short circuit condition to ground, despite thedestruction of the semiconductor device. Importantly, the fail-safefeature provided by the spring 70 is not triggered at any specifictemperature thereof, but is effective only when the semiconductormaterial liquefies. Accordingly, no safety margin is required or neededbetween the fail-safe operation and the temperature at which thesemiconductor material melts.

FIG. 4 illustrates the module housing 52 that is adapted forsnap-locking to the printed circuit board base 12. The housing 52includes a cover 80 that is shown for purposes of clarity in brokenline. The cover 80 is preferably formed of a valox plastic, or otherflameproof moldable material. The cover 80 is formed as a rectangularshell having an open bottom and a top handle 82 for easy grasping by aperson's fingers. At the bottom of the cover 80, near the opening, are apair of opposing wedge-shaped bosses, one shown as reference numeral 84.The boss 84 is formed integral on the inside surface of the cover 80,and includes a top surface 86 that is generally orthogonal to the insidesurface of the cover 80. The inside dimension of the cover 80 isselected so as to receive therein, in a close fit, therectangular-shaped printed circuit board base 12. By utilizing a pair ofbosses 84, the printed circuit board base 12 can be pushed into thebottom opening of the cover 80, and past the bosses 84 so as to besnap-locked and captured within the cover 80. When in a snap-lockposition, a bottom surface of the printed circuit board base 12 engageswith the top surface 86 of each of the bosses 84. Removal of the printedcircuit board base 12 can be achieved by using a blade slipped betweenthe edge of the printed circuit board base 12 and the inside surface ofthe cover 80 and prying the bosses 84 away from the printed circuitboard base 12. In this manner, the printed circuit board base 12 andassociated components can be removed from the housing 52.

Formed integral within the cover portion 80 of the housing 52 is a webconfiguration shown in solid line and as reference numeral 88. The webstructure 88 comprises a first planar web 90 and a second planar web 92interconnected by two partial-length webs 94 and 96, both shown inbroken line. As noted above, the web structure 88 is formed integralwith the cover 80 as a result of an injection molding process. At thelower end of each of the planar webs 90 and 92 there is a depending stopmember, one shown as reference numeral 98. The four stop members 98function to abut the top side of the printed circuit board 12 whenpushed into the open end of the cover 80. Each web 90 and 92 includes arecessed area 100 to accommodate the components, such as the conductivebridge 44 that extends above the surface of the printed circuit board12. The details of the enclosure 52, as well as the web structure 88 areshown more thoroughly throughout the views of FIGS. 5-10. The manner inwhich the webs 90 and 92, as well as the connecting webs 94 and 96 holdthe spring 46 in a fixed position is shown in more detail in FIGS. 11aand 11b.

The C-shape spring 46 is held in a fixed position within the cover 80between the planar webs 90 and 92, as well as abutted against theconnecting webs 94 and 96, as shown in FIGS. 11a and 11b. The C-shapespring 46 is generally captured between the spaced-apart planar webs 90and 92, as shown in FIG. 11b. The spring 46 loosely fits between thewebs 90 and 92 so as not to interfere with the movement of the springwhen the printed circuit board base and conductive bridge 44 are forcedthereagainst. This lateral engagement by the spring 46 constrains itfrom moving laterally. In FIG. 11a, the inside opposing surfaces of thecover 80 capture the spring to prevent movement in this direction. Theupper part of the spring 70 engages against the ends of the connectingwebs 94 and 96 and function as a stop to prevent the spring from movingupwardly. During tensioning of the spring 46 when the conductive bridge44 is forced in contact therewith, the semicircular ends 48 and 50 flexupwardly. In this manner the spring 46 is captured within the cover 80and a constant pressure is applied against the bridge 44 which, in turn,maintains the semiconductor devices 40 and 42 in electrical contact withthe respective conductive paths 14 and 28 of the printed circuit board12.

In accordance with another embodiment of the invention, the cover isfastened to the base in a permanent manner. As shown in FIG. 12, thereis illustrated a web structure 110, similar to that shown in connectionwith FIG. 4. For purposes of clarity, the cover of the module is notshown. In this embodiment, formed integral with the web structure 110 isplastic post 112 that extends below the stop members 114 a distancesufficient to protrude through a hole 116 in the printed circuit boardbase 118. Again, the various components mounted to the printed circuitboard base 118 are not shown. The post 112 extends beyond the bottomsurface of the base 118 when the latter is fully inserted into themodule cover and abutted against the stops 114. Then, the bottom end ofthe plastic post 112 is swaged by melting, or otherwise, to flare outthe end in a mushroomed manner and thereby fix the cover to the base118.

Various modifications can be made to the embodiments described above.For example, the conductive bridge 44 could be fabricated of aspring-like material to function also as a spring to force thesemiconductor devices 40 and 42 into contact with the respectiveconductive paths of the printed circuit board. With this arrangement,the spring conductive bridge would be fastened at its center to theprinted circuit board. Depending on the material with which the springconductive birdge is constructed, it could be soldered or screwed to theprinted circuit board. Also, those skilled in the art may prefer toconstruct either the conductive bridge 44, or the spring conductivebridge, in separate parts, one associated with each semiconductordevice.

In addition to the foregoing, the spring 46 can be made in manydifferent shapes and configurations for engagement with the internalstructure of the cover. Indeed, the spring 46 can be made as two or moreindividual spring components. By utilizing a spring structure thatengages internally with the cover, assembly of the module is facilitatedbecause fewer components need to be individually held in place at thesame time during overall assembly.

While the preferred and other embodiments of the invention have beendisclosed with reference to a specific telephone line protector device,and methods of fabrication and operation thereof, it is to be understoodthat many changes in detail may be made as a matter of engineeringchoices, without departing from the spirit and scope of the invention,as defined by the appended claims.

What is claimed is:
 1. A telephone line protection module having pinsextending exterior thereto and adapted for plugging into a socket,comprising:a base for said module defined by a printed circuit boardsupporting a plurality of said protection module pins, and conductivepaths formed on said printed circuit board, said protection module pinsbeing fixed in said printed circuit board base in electrical contactwith respective conductive paths; one or more overvoltage sensitivedevices in contact with respective said conductive paths so as toprovide overvoltage protection between ones of said protection modulepins and a protection module ground pin; and a spring under acompression pressure for holding each said overvoltage sensitive deviceinto said contact with a respective printed circuit board conductivepath.
 2. The telephone line protection module of claim 1, furtherincluding a conductive bridge disposed between said one or moreovervoltage sensitive devices and a ground conductor path, and whereinsaid spring biases said conductive bridge into contact with saidovervoltage sensitive device.
 3. The telephone line protection module ofclaim 2, wherein each said overvoltage sensitive device includesopposing surface contacts, only one of which makes contact through asoldered connection during conditions of no overvoltage, and another ofwhich makes contact by intimate contact.
 4. The telephone lineprotection module of claim 2, further including two overvoltagesensitive devices, and wherein said conductive bridge comprises a metalstrip bridging a top surface of both said devices to said groundconductor path.
 5. The telephone line protection module of claim 4,wherein said spring comprises a single spring wire having a C-shape,with the ends thereof curved.
 6. The telephone line protection module ofclaim 5, further including a module cover that has formed therein achannel guide for supporting said C-shape spring.
 7. The telephone lineprotection module of claim 1, wherein said printed circuit board has aplurality of holes therethrough for supporting said pins.
 8. Thetelephone line protection module of claim 1, further including a modulecover; wherein said module cover includes one or more plastic posts thatprotrude through a respective hole in said printed circuit board forfastening thereto.
 9. The telephone line protection module of claim 1,wherein each said overvoltage sensitive device is a semiconductor thatis not a packaged device.
 10. The telephone line protection module ofclaim 1, further including a protective cover snap-lockable to saidprinted circuit board.
 11. The telephone line protection module of claim10, wherein said protective cover has opposing shouldered bosses forengaging a bottom surface of said printed circuit board, and whereinsaid spring biases the printed circuit board against said shoulderedbosses to thereby provide a snap locking engagement of the protectivecover to the printed circuit board base.
 12. A telephone line protectionmodule having a module pins physically accessible outside said module,comprising:a printed circuit board base to which a plurality of theprotection module pins are mounted, including different conductive pathsformed on the printed circuit board to which the pins of the protectionmodule are electrically connected; a pair of semiconductor devices, eachhaving two contacts, and each semiconductor device being responsive toan overvoltage for conducting current, each semiconductor device beingarranged so as to contact a printed circuit board conductive pathassociated with one said protection module pin and conduct current to aprotection module ground pin in response to an overvoltage; at least oneconductive bridge providing a connection between another contact of eachsaid semiconductor device and the ground pin; a module cover engageablewith said printed circuit board base; and a compression spring disposedbetween said module cover and each said conductive bridge so as todeform said semiconductor device during a thermal failure thereof andcause the respective bridge to be short-circuited to a conductive pathof the printed circuit board.
 13. The telephone line protection moduleof claim 12, further including a single spring wire with two ends, eachend being spring biased between said module cover and a respective saidconductive bridge.
 14. The telephone line protection module of claim 12,wherein each said semiconductor device is not encapsulated in a packagedmaterial.
 15. The telephone line protection module of claim 12, whereinsaid module cover is snap-fit to said printed circuit board base. 16.The telephone line protection module of claim 12, wherein each saidbridge comprises a single conductor strap in electrical contact withboth said semiconductor devices and a grounded conductive path.
 17. Thetelephone line protection module of claim 12, wherein a first conductivepath short-circuits two said pins, and a second said conductive pathsshort circuits two other pins.
 18. The telephone line protection moduleof claim 17, wherein said first conductive path provides an electricalcontact to one said semiconductor device at a location between said twopins.
 19. The telephone line protection module of claim 12, wherein saidmodule cover is formed with an inside slot to capture and support atleast a portion of said spring.
 20. A telephone line protection module,comprising:a protective cover; a plurality of protection module pinsextending from said protection module and connectable to a socket; aprinted circuit board having conductive paths electrically connected torespective said protection module pins; two semiconductor devices, eachhaving at least two contact pads, and each semiconductor device beingresponsive to respective overvoltage conditions to provide a lowresistance path between respective contact pads of said semiconductordevices, a first contact pad of each said semiconductor device being indirect contact with a respective conductive path of said printed circuitboard; and a conductive bridge connected directly to a conductive pathof said printed circuit board that is connected to a ground pin of saidprotection module, a respective portion of said conductive bridgeoverlying and electrically connected to each said semiconductor device.21. The telephone line protection module of claim 20, wherein saidprinted circuit board has holdes therethrough, and said protectionmodule pins extend through said printed circuit board holes.
 22. Thetelephone line protection module of claim 20, wherein said conductivebridge has a center portion thereof which is soldered to a conductivepath of said printed circuit board, and two ends extending from thecenter portion, each said end overlying a respective said semiconductordevice.